Severe systemic inflammation (SSI) with multiorgan dysfunction from sepsis or non infectious agents is a disease with major mortality and morbidity. SSI is associated with gene-specific reprogramming of innate immunity leukocyte responses to Toll-like receptor (TLR)-4dependent signaling, which epigenetically represses transcription of a set of acute proinflammatory genes, while activating other sets of genes that generate anti- inflammatory mediators and anti-microbial peptides. This gene reprogramming is important in at least two ways. Its presence indicates repressed innate and adaptive immunity and its reversal correlates with improved outcomes in SSI in humans and animals. We have reported that the epigenetic silencing signature requires Toll-like receptor 4 (TLR4) induction of NF-kappa B factor RelB that disrupts p65 promoter binding, directs histone H3K9 di-methylation by G9a to provide a binding site of heterochromatin protein 1 (HP1), which then links to DNA CpG methylation responses and chromatin structural proteins. This RelB-dependent process alters the state of responsive euchromatin to produce silenced facultative heterochromatin. The general objective of our research is to define mechanisms that shift chromatin between the euchromatin and facultative heterochromatin states. This proposal tests the hypothesis that G9a and RelB provide a bond for both assembling and disassembling facultative heterochromatin during SSI by its ability to directly bind G9a, which couples to histone and DNA modifiers and structural chromatin proteins like linker histone H1 and high mobility group box 1 (HMGB1) proteins. Aim 1 will test for direct interaction and feedback between G9a and RelB to initiate and reverse gene-specific change from active euchromatin to facultative heterochromatin at the proximal promoters of acute proinflammatory genes TNFa and IL-1b. Aim 2 will test whether the linker histone H1, in concert with HMGB1, sustains heterochromatin assembly and transcription silencing by re-positioning nucleosomes and maintaining RelB and G9a binding at promoter sequences of TNFa and IL-1b. Aim 3 will use human peripheral blood leukocytes to extend the gene-specific reprogramming paradigm to human SSI. Our experimental approaches will employ genetic and biochemical analyses.]